High pressure discharge lamp lighting apparatus and high pressure discharge lamp lighting method

ABSTRACT

A high pressure discharge lamp lighting apparatus is provided which prevents dying out or instabilities of the discharge arc inside the arc tube due to the acoustic resonance phenomena and enables to light the high pressure discharge lamp in a steady state. In the high pressure discharge lamp lighting apparatus having the high pressure discharge lamp, the lamp voltage detecting device, the high frequency power supplying device, and the control circuit, the apparatus includes an extracting device for extracting an upper limit frequency and a lower limit frequency of the resonance-free frequency band, and the control circuit includes a frequency moving device for changing the frequency of the high frequency power within a range defined by the upper limit frequency and the lower limit frequency extracted by the extracting device and then moving the frequency to a predetermined frequency which is determined based on the upper limit frequency and the lower limit frequency.

TECHNICAL FIELD

The present invention relates to a high pressure discharge lamp lightingapparatus for lighting a high pressure discharge lamp at highfrequencies.

BACKGROUND ART

FIG. 17 shows a circuit configuration of a high pressure discharge lamplighting apparatus of a conventional art. In FIG. 17, the high pressuredischarge lamp lighting apparatus includes a direct current power source1, a half bridge circuit 2 consisting of a first switching element 2 aand a second switching element 2 b for converting direct current voltageof the direct current power source 1 to high frequency voltage, acontrol circuit 3 for controlling ON/OFF operation of each switchingelement forming the half bridge circuit 2, a load circuit 4 including aresonant condenser 5, a chalk coil 6, and a starting circuit 7, and ahigh pressure discharge lamp 8 which is lit by the high frequencyvoltage supplied from the load circuit 4.

In the high pressure discharge lamp lighting apparatus including theabove configuring elements, the operation of each switching component iscontrolled by the control circuit 3 so as to supply the high frequencyvoltage having equal to or greater than 1 kHz to the high pressuredischarge lamp 8 via a load circuit 4. Further, the control circuit 3controls the operation of each in order to prevent generation ofacoustic resonance phenomena such as “dying out” or “instabilities”accompanied to a bend of a discharge arc inside an arc tube of the highpressure discharge lamp 8, which is well known.

The conventional lighting apparatus for a high pressure discharge lampemploys a configuration which lights the high pressure discharge lamp bysetting the lighting frequency to the resonance-free frequency asdiscussed above. However, it is known to the public that the speed ofsound wave within the arc tube changes according to an accumulatedlighting time in the high pressure discharge lamp or that theresonance-free frequency band also changes as an electrode exhausts.Conventionally, there has been a problem the high pressure dischargelamp generates the acoustic resonance phenomena such as “dying out” or“instabilities” according to the bend of the discharge arc within thearc tube due to the above various reasons, which prevents the highpressure discharge lamp from keeping steady state lighting.

The present invention aims to solve the above problems and to providethe high pressure discharge lamp lighting apparatus, which always canprevent “dying out” and “instabilities” of the discharge arc within thearc tube even if the resonance-free frequency changes due to the abovevarious factors, and can light the high pressure discharge lamp in asteady state at high frequencies.

DISCLOSURE OF THE INVENTION

According to the present invention, a high pressure discharge lamplighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus includes anextracting means for extracting an upper limit frequency and a lowerlimit frequency of resonance-free frequency band,

the control circuit includes a frequency moving means for changing thefrequency of the high frequency power in a range defined by the upperlimit frequency and the lower limit frequency, and for moving thefrequency to a frequency determined based on the upper limit frequencyand the lower limit frequency.

Further, in a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means,

the control circuit includes:

a frequency storing means for storing a first frequency of a point whena lamp voltage of the high pressure discharge lamp begins increasing incase that the frequency of the high frequency power is made decreaseafter the high pressure discharge lamp is lit at the predeterminedfrequency and a second frequency of a point when the lamp voltage of thehigh pressure discharge lamp begins increasing in case that thefrequency of the high frequency power is made increase; and

a frequency moving means for moving the frequency of the high frequencypower to a third frequency which is determined based on the firstfrequency and the second frequency stored in the frequency storingmeans.

Further, in a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means,

the control circuit includes:

a lamp voltage storing means for storing a lamp voltage of a point whenthe high pressure discharge lamp is lit at a predetermined frequency;

a frequency storing means for storing a first frequency of a point whenthe lamp voltage of the high pressure discharge lamp exceeds the lampvoltage stored in the lamp voltage storing means in case that thefrequency of the high frequency power is made decrease and a secondfrequency of a point when the lamp voltage of the high pressuredischarge lamp exceeds the lamp voltage stored in the lamp voltagestoring means in case that the frequency of the high frequency power ismade increase; and

a frequency moving means for moving the frequency of the high frequencypower to a third frequency which is determined based on the firstfrequency and the second frequency stored in the frequency storingmeans.

Further, the control circuit limits a moving range of a series ofdecreasing the frequency of the high frequency power after the highpressure discharge lamp is lit at a predetermined frequency, increasingthe frequency of the high frequency power, and moving the frequency ofthe high frequency power to a lighting frequency which is determinedbased on the frequencies.

Further, the frequency moving means repeatedly performs a series ofoperation of moving the frequency of the high frequency power at apredetermined interval.

Further, the control circuit sets the predetermined frequency of thepoint when the high pressure discharge lamp is lit so as to match alighting frequency of a previous lighting before turning-off.

Further, a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus lights thehigh pressure discharge lamp in a steady state within a particularfrequency range and a particular voltage range of a resonance-freeregion which is determined by the lamp voltage and a resonance-freefrequency band corresponding the lamp voltage,

the high pressure discharge lamp lighting apparatus includes a resonancestrength detecting means for detecting rate of a instabilities of adischarge arc due to acoustic resonance phenomena based on a change ofthe lamp voltage detected by the lamp voltage detecting means,

the high pressure discharge lamp applies a first frequency which islower than a maximum frequency of the particular frequency range as alighting frequency at lighting time, and

when the resonance strength detecting means detects the instabilities ofthe discharge arc which exceeds a predetermined rate accompanied toincrease of the lamp voltage after lighting, the control circuitincreases the lighting frequency by a predetermined amount from thefirst frequency and switches the lighting frequency to a secondfrequency which belongs to the resonance-free region.

Further, when the resonance strength detecting means does not detect theinstabilities of the discharge arc which exceeds the predetermined rateeven if a predetermined time has passed since starting lightingoperation, the control circuit forcibly switches the lighting frequencyfrom the first frequency to the second frequency.

Further, a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus lights thehigh pressure discharge lamp in a steady state within a particularfrequency range and a particular voltage range of a resonance-freeregion which is determined by the lamp voltage and a resonance-freefrequency band corresponding the lamp voltage,

the high pressure discharge lamp lighting apparatus includes a resonancestrength detecting means for detecting rate of instabilities of adischarge arc due to acoustic resonance phenomena based on a change ofthe lamp voltage detected by the lamp voltage detecting means,

the high pressure discharge lamp applies a first frequency which islower than a maximum frequency of the particular frequency range as alighting frequency at lighting time, and

when the lamp voltage detecting means detects one of that the lampvoltage exceeds a predetermined value after lighting and that apredetermined time has passed since a lighting operation has started,the control circuit increases the lighting frequency by a predeterminedamount from the first frequency and switches the lighting frequency to asecond frequency which belongs to the resonance-free region.

Further, after switching the lighting frequency from the first frequencyto the second frequency, the control circuit gradually or continuouslydecrease the second frequency in respect of an increase of the lampvoltage.

Further, a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus lights thehigh pressure discharge lamp in a steady state within a particularfrequency range and a particular voltage range of a resonance-freeregion which is determined by the lamp voltage and a resonance-freefrequency band corresponding the lamp voltage,

the high pressure discharge lamp lighting apparatus includes a resonancestrength detecting means for detecting rate of instabilities of adischarge arc due to acoustic resonance phenomena based on a change ofthe lamp voltage detected by the lamp voltage detecting means,

the high pressure discharge lamp applies a first frequency which islower than a maximum frequency of the particular frequency range as alighting frequency at lighting time, and

when the resonance strength detecting means detects the instabilities ofthe discharge arc which exceeds a predetermined rate according toincrease of the lamp voltage after lighting, the control circuitdecreases the lighting frequency by a predetermined amount from thefirst frequency and switches the lighting frequency to a secondfrequency which belongs to the resonance-free region and makes thesecond frequency gradually or continuously decrease in respect of theincrease of the lamp voltage within the resonance-free region.

Further, a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus lights thehigh pressure discharge lamp in a steady state within a particularfrequency range and a particular voltage range of a resonance-freeregion which is determined by the lamp voltage and a resonance-freefrequency band corresponding the lamp voltage,

the high pressure discharge lamp lighting apparatus includes a resonancestrength detecting means for detecting rate of instabilities of adischarge arc due to acoustic resonance phenomena based on a change ofthe lamp voltage detected by the lamp voltage detecting means,

the high pressure discharge lamp applies a first frequency which islower than a maximum frequency of the particular frequency range as alighting frequency at lighting time,

when the lamp voltage detecting means detects one of that the lampvoltage exceeds a predetermined value after lighting and that apredetermined time has passed since a lighting operation has started,and

when the resonance strength detecting means detects the instabilities ofthe discharge arc which exceeds a predetermined rate according toincrease of the lamp voltage after lighting, the control circuitdecreases the lighting frequency by a predetermined amount from thefirst frequency and switches the lighting frequency to a secondfrequency which belongs to the resonance-free region and makes thesecond frequency gradually or continuously decrease in respect of theincrease of the lamp voltage within the resonance-free region.

Further, the control circuit performs an operation of graduallydecreasing the second frequency by repeatedly decreasing the lightingfrequency by a predetermined amount when the resonance strengthdetecting means detects the instabilities of the discharge arc whichexceeds the predetermined rate accompanied to an increase of the lampvoltage.

Further, the control circuit performs an operation of graduallydecreasing the second frequency by decreasing the lighting frequency andthen repeatedly increasing the lighting frequency by the predeterminedamount with a predetermined interval when the resonance strengthdetecting means detects the instabilities of the discharge arc whichexceeds the predetermined rate accompanied to a decrease of the tubelighting frequency.

Further, the control circuit performs an operation of continuouslydecreasing the second frequency by controlling to decrease the lightingfrequency with approximately fixed changing rate in respect of anincrease of the lamp voltage.

Yet further, a high pressure discharge lamp lighting apparatus having:

a high pressure discharge lamp;

a lamp voltage detecting means for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp;

a control circuit for controlling a frequency of the high frequencypower supplied by the high frequency power supplying means, and

wherein the high pressure discharge lamp lighting apparatus lights thehigh pressure discharge lamp in a steady state within a particularfrequency range and a particular voltage range of a resonance-freeregion which is determined by the lamp voltage and a resonance-freefrequency band corresponding to the lamp voltage,

the high pressure discharge lamp applies a first frequency which ishigher than a maximum frequency of the particular frequency range as alighting frequency and decreases the lighting frequency at approximatelyfixed rate so as to stay within the resonance-free region in respect ofan increase of the lamp voltage.

According to the present invention, a method for a high pressuredischarge lamp lighting having:

a high pressure discharge lamp;

a lamp voltage detecting step for detecting a lamp voltage of the highpressure discharge lamp;

a high frequency power supplying step for supplying high frequency powerto the high pressure discharge lamp;

a control step for controlling a frequency of the high frequency powersupplied by the high frequency power supplying means,

the method includes an extracting step for extracting an upper limitfrequency and a lower limit frequency from a resonance-free frequencyband, and

the control step changes a frequency of the high frequency power withina range defined by the upper limit frequency and the lower limitfrequency of the resonance-free frequency band extracted by theextracting means, and then moves to a predetermined frequency which isdetermined based on the upper limit frequency and the lower limitfrequency.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows a circuit configuration of a high pressure discharge lamplighting apparatus according to the first embodiment of the presentinvention.

FIG. 2 is a flow chart showing a flow of an operation of the highpressure discharge lamp lighting apparatus of the first embodiment.

FIG. 3 is a timing chart showing a timing of the operation of the highpressure discharge lamp lighting apparatus of the first embodiment.

FIG. 4 is a timing chart showing a timing of another operation of thehigh pressure discharge lamp lighting apparatus of the first embodiment.

FIG. 5 is a flow chart showing a flow of an operation of the highpressure discharge lamp lighting apparatus of the second embodiment.

FIG. 6 is a timing chart showing a timing of the operation of the highpressure discharge lamp lighting apparatus of the second embodiment.

FIG. 7 is a flow chart showing a flow of an operation of the highpressure discharge lamp lighting apparatus of the third embodiment.

FIG. 8 is a timing chart showing a timing of the operation of the highpressure discharge lamp lighting apparatus of the third embodiment.

FIG. 9 shows a circuit configuration of a high pressure discharge lamplighting apparatus according to the fourth embodiment of the presentinvention.

FIG. 10 shows a trace L1 of an operation point of the high pressuredischarge lamp lighting apparatus according to the fourth embodiment.

FIG. 11 shows a trace L2 of an operation point of the high pressuredischarge lamp lighting apparatus according to the fifth embodiment.

FIG. 12 shows a trace L3 of an operation point of the high pressuredischarge lamp lighting apparatus according to the sixth embodiment.

FIG. 13 shows a trace L4 of an operation point of the high pressuredischarge lamp lighting apparatus according to the seventh embodiment.

FIG. 14 shows a trace L5 of an operation point of the high pressuredischarge lamp lighting apparatus according to the eighth embodiment.

FIG. 15 shows a trace L6 of an operation point of the high pressuredischarge lamp lighting apparatus according to the eighth embodiment.

FIG. 16 shows a trace L7 of an operation point of the high pressuredischarge lamp lighting apparatus according to the eighth embodiment.

FIG. 17 shows a configuration circuit of a conventional high pressuredischarge lamp lighting apparatus.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiment 1.

FIG. 1 shows a circuit configuration of a high pressure discharge lamplighting apparatus according to the first embodiment. Different from theconventional apparatus, in FIG. 1, the high pressure discharge lamplighting apparatus includes a lamp voltage detecting circuit 9 and acontrol circuit 10. The lamp voltage detecting circuit 9 detects a lampvoltage of a high pressure discharge lamp 8. The control circuit 10extracts resonance-free frequency that does not generate acousticresonance phenomena from a value (a value of the lamp voltage) detectedby the lamp voltage detecting circuit 9 and controls the operationalfrequencies of switching elements 2 a and 2 b composing a half bridgecircuit 2 so that the lighting frequency matches the extractedresonance-free frequency.

The lighting operation of the high pressure discharge lamp lightingapparatus having the above configuration will be explained by referringto the circuit configuration of FIG. 1 and a flow chart showing the flowof the operation of FIG. 2. In case that the operation of the lightingapparatus is started (at step S100), on starting lighting the highpressure discharge lamp 8, the control circuit 10 previously controlsthe operational frequency of each switching element composing the halfbridge circuit 2 so that an initial lighting frequency f0 matches theresonance-free frequency fx and lights the high pressure discharge lamp8 (at step S101). Then, the control circuit 10 decreases the lightingfrequency by changing the operational frequencies of the switchingelements 2 a and 2 b (at step S102). The control circuit 10 observes thevalues detected by the lamp voltage detecting circuit 9.

The control circuit 10 judges if the detected value of the lamp voltagedetecting circuit 9, namely, the lamp voltage of the high pressuredischarge lamp 8 starts increasing (at step S103). Here, when thelighting frequency becomes close to the acoustic resonant frequency bandthat generates the acoustic resonance phenomena, the lamp voltage of thehigh pressure discharge lamp 8 increases. For this reason, when the lampvoltage of the high pressure discharge lamp 8 does not increase (NO atstep S103), the control circuit 10 further decreases the lightingfrequency (at step S102), and the above operation is repeated. On theother hand, when the fact that the lamp voltage of the high pressuredischarge lamp 8 increases is detected (YES at step S103), the controlcircuit 10 stops decreasing the lighting frequency and records thelighting frequency f1 at this time (at step S104).

Next, the control circuit 10 increases the lighting frequency from f1 asa basic point in the above operation (at step S105) and observes thevalues detected by the lamp voltage detecting circuit 9. The controlcircuit 10 judges if the lamp voltage of the high pressure dischargelamp 8 detected by the lamp voltage detecting circuit 9 startsincreasing (at step S106). When the lamp voltage of the high pressuredischarge lamp 8 does not increase, the control circuit 10 furtherincreases the lighting frequency (at step S105), and the above operationis repeated. On the other hand, when the fact that the lamp voltage ofthe high pressure discharge lamp 8 increases is detected, the controlcircuit 10 stops increasing the lighting frequency and records thelighting frequency f2 at this time (at step S107).

Next, the control circuit 10 obtains an intermediate frequency fx by anequation fx=(f1+f2)/2 using the two lighting frequencies f1 and f2 whichhave been recorded above. The control circuit 10 controls the operationof each switching element of the half bridge circuit 2 so that thelighting frequency becomes the calculated lighting frequency fx andlights the high pressure discharge lamp 8 (at step S108). Because ofthis, it becomes possible to light the high pressure discharge lamp 8 inthe resonance-free frequency band. And then, the control circuit 10judges if the operation of the lighting apparatus finishes or not (atstep S109). Here, when the control circuit 10 judges the operation hasnot been finished and a signal to turn off the light is not sent to thelighting apparatus (NO at the step S109), the control circuit 10 keepslighting of the high pressure discharge lamp 8 at the lighting frequencyfx.

After a predetermined interval (at step S110), the control circuit 10changes the operational frequency of the half bridge circuit 2 again todecrease the lighting frequency from fx as a basic point (at step S102).Hereinafter, the above operations (from step S103 through S110) arerepeated sequentially. When it is judged that the turning-off signal hasbeen sent to the lighting apparatus (YES at step S109), the operation ofthe lighting apparatus terminates (at step 111). By these operation forlighting, a band in which the lamp voltage of the high pressuredischarge lamp 8 is always low is extracted, which enables to make thelighting frequency match the resonance-free frequency.

Here, in the flowchart of FIG. 2, the control circuit 10 memorizes theabove lighting frequency fx directly before the completion (at stepS111) of the lighting operation in a non-volatile memory stored in thecontrol circuit 10. And then, the control circuit 10 can perform thelighting operation using the lighting frequency fx by reading thelighting frequency fx from the non-volatile memory at starting time ofthe next lighting operation (at step S100). This can be applied to thesecond embodiment, which will be discussed below.

The lighting operation of the high pressure discharge lamp lightingapparatus will be explained by referring to FIGS. 3 and 4, which aretiming charts showing characteristics of the lamp voltage in respect ofthe decrease/increase of the lighting frequency. FIG. 3 shows an exampleof characteristics of the high pressure discharge lamp 8, in which thelamp voltage in respect of the decrease/increase of the lightingfrequency in the resonance-free frequency band is low and the frequencyband to keep a predetermined level is wide. In FIG. 3, at startinglighting operation of the high pressure discharge lamp 8, the controlcircuit 10 lights the lamp by setting the lighting frequency to f0 whichmatches to the resonance-free frequency, and then decreases the lightingfrequency. At a point when the lighting frequency is f1, the lampvoltage begins to increase, and the control circuit 10 stops changingthe lighting frequency.

Next, by increasing the lighting frequency from f1 as a basic point, thelamp voltage begins to increase at the point when the lighting frequencyis f2, and the control circuit 10 stops changing the lighting frequency.Subsequently, at the point when the lighting frequency is fx between thelighting frequencies f1 and f2 in the frequency band, namely, anintermediate point of the resonance-free frequency band, the controlcircuit 10 continues the lighting operation of the high pressuredischarge lamp 8 for a predetermined time. Then, by increasing thelighting frequency after decreasing again from fx as the basic point,the control circuit 10 controls to light the high pressure dischargelamp 8 around the intermediate point of the resonance-free frequencyband of the frequency band, in which the lamp voltage is always low andthe predetermined level is kept. The time required for changing thelighting frequency from f0 as the basic point to f1, from f1 to f2, fromf2 to fx can vary as long as it is visually unrecognizable.

FIG. 4 shows an example of characteristics of the high pressuredischarge lamp 8, in which the lamp voltage in respect of thedecrease/increase of the lighting frequency in the resonance-freefrequency band is low and the frequency band to keep a predeterminedlevel is rare. In FIG. 4, at starting the lighting operation of the highpressure discharge lamp 8, the control circuit 10 lights the lamp bysetting the lighting frequency to f0 and then changes the lightingfrequency by decreasing it. At a point when the lighting frequency isf1, which is close to f0, the lamp voltage begins to increase, and thecontrol circuit 10 stops changing the lighting frequency. Next, byincreasing the lighting frequency from f1 as a basic point, the lampvoltage begins to increase at the point when the lighting frequency isf2, and the control circuit 10 stops changing the lighting frequency.Subsequently, at the point when the lighting frequency is fx between thelighting frequencies f1 and f2 in the frequency band, namely, anintermediate point of the resonance-free frequency band, the controlcircuit 10 continues the lighting operation of the high pressuredischarge lamp 8 for the predetermined time. Hereinafter, the operationwill be the same as discussed above. In this way, the high pressuredischarge lamp 8 can be always lit at the intermediate point of theresonance-free frequency band.

In another way, the control circuit 10 can set the lighting frequency tof0 at the time of starting the lighting operation, and then the controlcircuit 10 can set a changing rate to decrease/increase the lightingfrequency by indicating the range with percentage to the lightingfrequency f0 such as ± some %.

In the above description of the operation, the lighting frequency isdecreased and then increased; however, the lighting frequency can beincreased and then decreased. This can be applied to the second and thethird embodiments, which will be discussed below.

As has been described, based on the lamp voltage of the high pressuredischarge lamp 8, the resonance-free frequency band is extracted, andthe light is lit at the lighting frequency fx, which is an intermediatepoint of the extracted band. Accordingly, even if the resonance-freefrequency band is moved by, for example, aging of the high pressuredischarge lamp 8, it is always possible to prevent generation of “dyingout” or “instabilities” of the discharge arc and to light the highpressure discharge lamp 8 in a steady state.

In this way, according to the present embodiment, the high pressuredischarge lamp lighting apparatus and the high pressure discharge lamplighting method having: the high pressure discharge lamp; the lampvoltage detecting means for detecting the lamp voltage of the highpressure discharge lamp; the high frequency power supplying means forsupplying the high frequency power to the high pressure discharge lamp;and the control circuit 10 for controlling the frequency of the highfrequency power supplied by the high frequency power supplying means,the apparatus and the method includes an extracting means for extractingan upper limit frequency and a lower limit frequency of thenon-resonance frequency band, and the control circuit 10 includes afrequency moving means for changing the frequency of the high frequencypower within a range between the upper limit frequency and the lowerlimit frequency of the resonance-free frequency band extracted by theextracting means, and then moving the frequency to a predeterminedfrequency decided based on the upper limit frequency and the lower limitfrequency. Accordingly, even if the resonance-free frequency band ismoved by, for example, aging of the high pressure discharge lamp, it ispossible to supply the high frequency power having the intermediatefrequency of the range to the high pressure discharge lamp, whichprevents generation of “dying out” or “instabilities” of the dischargearc inside the arc tube and enables to light the high pressure dischargelamp in a steady state.

Further, in the high pressure discharge lamp lighting apparatus havingthe high pressure discharge lamp; the high frequency power supplyingmeans; and the control circuit 10 for controlling the frequency of thehigh frequency power supplied by the high frequency power supplyingmeans, the control circuit 10 includes a frequency memorizing means formemorizing a first frequency at a point when the lamp voltage of thehigh pressure discharge lamp begins to increase when the control circuit10 decreases the frequency of the high frequency power after lightingthe high pressure discharge lamp with the predetermined frequency and asecond frequency at a point when the lamp voltage of the high pressuredischarge lamp begins to increase when the control circuit 10 increasesthe frequency of the high frequency power; and a frequency moving meansfor moving the frequency of the high frequency power to a thirdfrequency determined based on the first frequency and the secondfrequency memorized in the frequency memorizing means. Accordingly, evenif the resonance-free frequency band is moved by aging of the highpressure discharge lamp, etc. it is always possible to supply the highfrequency power having the intermediate frequency of the range to thehigh pressure discharge lamp, which prevents generation of “dying out”or “instabilities” of the discharge arc inside the arc tube and enablesto light the high pressure discharge lamp in a steady state.

Further, the frequency moving means repeatedly performs a series ofoperations for moving the frequency of the high frequency power with apredetermined interval, which enables to always prevent generation ofacoustic resonance phenomena even if the resonance-free frequency bandis moved and to light the high pressure discharge lamp in a steadystate.

Further, the control circuit 10 is configured so that the predeterminedfrequency at the time of lighting the high pressure discharge lampmatches to the lighting frequency before the previous turn-off, whichenables to prevent generation of “dying out” or “instabilities” of thedischarge arc inside the arc tube and enables to light the high pressuredischarge lamp in a steady state.

Embodiment 2.

FIG. 5 is a flowchart showing an operation flow of the high pressuredischarge lamp according to the second embodiment. Here, the circuitconfiguration of the high pressure discharge lamp lighting apparatus isthe same as one of the first embodiment.

Next, a lighting operation of the high pressure discharge lamp havingthe above configuration will be explained by referring to the flowchartof FIG. 5. In case of starting the operation of the lighting apparatus(at step S200), on starting lighting the high pressure discharge lamp 8,the control circuit 10 sets an initial lighting frequency f0 so as tomatch the resonance-free frequency fx and lights the high pressuredischarge lamp 8 (at step S201). And the control circuit 10 lights thehigh pressure discharge lamp 8 at the lighting frequency f0 and sets thelamp voltage V0 at this time. Afterwards, the control circuit 10decreases the lighting frequency (at step S203) and observes a valuedetected by the lamp voltage detecting circuit 9.

Next, the control circuit 10 judges if the value detected by the lampvoltage detecting circuit 9, namely, the increased lamp voltage Vx ofthe high pressure discharge lamp 8 is larger than the lamp voltage V0 ornot (at step S204). When the lamp voltage Vx is judged to be smallerthan the lamp voltage V0 (NO at step S204), the control circuit 10continues to change the lighting frequency by decreasing it (at stepS203). When the lamp voltage Vx is judged to be larger than the lampvoltage V0 (YES at step S204), the control circuit 10 assumes that thelighting frequency becomes close to the acoustic resonant frequency bandthat is out of the resonance-free frequency band and stops changing thelighting frequency by decreasing it. Then, the control circuit 10memorizes the lighting frequency f1 at this time (at step S205).

Subsequently, the control circuit 10 changes the lighting frequency byincreasing it (at step S206) and judges if the lamp voltage Vx is largerthan the lamp voltage V0 or not (at step S207). In case of NO at stepS207, the control circuit 10 assumes the lamp voltage Vx is smaller thanthe lamp voltage V0 and continues to change the lighting frequency (atstep S206). In case of YES at step S207, the control circuit 10 assumesthat the lighting frequency becomes close to the acoustic resonantfrequency region by the fact that the lamp voltage Vx is larger than thelamp voltage V0 and stops changing the lighting frequency by increasingit. Then, the control circuit 10 memorizes the lighting frequency f2 atthis time (at step S208). Next, the control circuit 10 obtains anintermediate frequency fx between the lighting frequencies f1 and f2 bycalculating an equation, fx=(f1+f2)/2 and lights the high pressuredischarge lamp 8 with this frequency fx (at step S209). Hereinafter, theoperations (steps S210 through 212) are the same as one of the firstembodiment and an explanation is omitted.

The operation will be explained by referring to FIG. 6, which is atiming chart showing characteristics of the lamp voltage in respect ofthe decrease/increase of the lighting frequency. FIG. 6 shows an exampleof characteristics of the high pressure discharge lamp 8, in which thelamp voltage is low and the frequency band to keep a predetermined levelof lighting is little. In FIG. 6, the control circuit 10 lights the highpressure discharge lamp 8 at the lighting frequency f0 and then changesthe lighting frequency by decreasing it. Just after starting decreasingthe lighting frequency, at a point when the lighting frequency is f1,the lamp voltage Vx begins to exceed the lamp voltage V0, and thecontrol circuit 10 stops changing the lighting frequency. Next thecontrol circuit 10 increases the lighting frequency from f1 as a basicpoint. Then, the lamp voltage Vx begins to exceed the lamp voltage V0 atthe point when the lighting frequency is f2, and the control circuit 10stops changing the lighting frequency.

Subsequently, at the point when the lighting frequency is fx, namely, anintermediate point of the lighting frequencies f1 and f2 in theresonance-free region, the control circuit 10 continues the lightingoperation of the high pressure discharge lamp 8 for the predeterminedtime. And then, the control circuit 10 stops decreasing the lightingfrequency when the lamp voltage Vx begins to exceed the lamp voltage V0,which is the lamp voltage value when the lighting frequency is fx,during the process of decreasing the lighting frequency again from thelighting frequency fx as the basic point. Hereinafter, the controlcircuit 10 changes the lighting frequency in the same manner asdiscussed above. By changing the lighting frequency withdecreasing/increasing it, the operation is controlled so as to light thehigh pressure discharge lamp 8 at the intermediate point of theresonance-free frequency band, namely, at the point when the lampvoltage is the lowest.

Applying the above control method for decreasing/increasing the lightingfrequency, the lighting apparatus is configured to light the lamp at theintermediate lighting frequency fx of the resonance-free frequency band,so that it is always possible to light the high pressure discharge lamp8 in a steady state even if the resonance-free frequency band is moveddue to the aging of the high pressure discharge lamp 8, etc.

In this way, according to the present embodiment, in the high pressuredischarge lamp lighting apparatus and the high pressure discharge lamplighting method having the high pressure discharge lamp; the highfrequency power supplying means for supplying the high frequency powerto the high pressure discharge lamp; and the control circuit forcontrolling the frequency of the high frequency power supplied by thehigh frequency power supplying means, the control circuit includes alamp voltage storing means for storing the lamp voltage of the time whenthe high pressure discharge lamp is lit at the predetermined frequency,a frequency storing means for storing a first frequency at a point whenthe lamp voltage of the high pressure discharge lamp begins to exceedthe lamp voltage stored by the lamp voltage storing means when thecontrol circuit decreases the frequency of the high frequency power anda second frequency at a point when the lamp voltage of the high pressuredischarge lamp begins to exceed the lamp voltage stored by the lampvoltage storing means when the control circuit increases the frequencyof the high frequency power; and a frequency moving means for moving thefrequency of the high frequency power to a third frequency determinedbased on the first frequency and the second frequency stored in thefrequency storing means. Accordingly, even if the resonance-freefrequency band is moved due to the aging of the high pressure dischargelamp, etc. it is possible to prevent “dying out” or “instabilities” ofthe discharge arc inside the arc tube and to light the high pressuredischarge lamp in a steady state.

Embodiment 3.

FIG. 7 is a flowchart showing an operation flow of the high pressuredischarge lamp lighting apparatus according to the third embodiment. Thecircuit configuration of the high pressure discharge lamp lightingapparatus is the same as one of the first embodiment.

In the following, a lighting operation of the high pressure dischargelamp lighting apparatus having this configuration will be explained byreferring to the flowchart of FIG. 7. In case of starting operation ofthe lighting apparatus (step S300), the control circuit 10 lights thehigh pressure discharge lamp 8 by previously setting the high pressuredischarge lamp 8 to an arbitrary frequency fx1 which matches theresonance-free frequency (step S301). Then, the control circuit 10checks if the lamp voltage of the high pressure discharge lamp 8 hasincreased or not using the lamp voltage detecting circuit 9 and checksif the lighting frequency has approached the acoustic resonant frequencyband that is off the resonance-free region (step S302). Here, in case ofNO at step S302, the control circuit 10 continues to light the highpressure discharge lamp 8 at the lighting frequency fx1 (step S301).

Next, in case of YES at step S302, the control circuit 10 changes thelighting frequency of the high pressure discharge lamp 8 by decreasingit to the frequency that is equal to fx1−α (step S303). Then, thecontrol circuit 10 increases the lighting frequency to the frequencythat is equal to fx1+β (step S304). Subsequently, in the process ofchanging the decrease of the lighting frequency to the increase, thecontrol circuit 10 stores the frequency of a point corresponding to theminimum lamp voltage as a new value of fx1, and performs the lightingoperation at this frequency fx1 (step S305). Next, the control circuit10 sets the lighting frequency fx1 in the non-volatile memory (stepS306). The subsequent operations (steps S307 through 308) are the sameas ones in the first embodiment and the explanation is omitted here.

Further, the operation will be explained by referring to FIG. 8, whichis a timing chart showing characteristics of the lamp voltage in respectof the decrease/increase of the lighting frequency. FIG. 8 shows anexample of the characteristics of the high pressure discharge lamp 8, ofwhich the lamp voltage of the resonance-free frequency band has a formwith multiple convexes and concaves. In FIG. 8, the control circuit 10performs the lighting operation by setting the lighting frequency to fx1at starting, and after decreasing the lighting frequency to, forexample, fx1−2 kHz, the control circuit 10 increases to fx1+2 kHz. Thecontrol circuit 10 stores the lighting frequency fx2 that is thefrequency of the point at which the lamp voltage becomes the minimumduring the process, and the lighting operation is continued at thefrequency fx2. Next, in case of detecting the increase of the lampvoltage by the lamp voltage detecting circuit 9, the control circuit 10decreases the frequency from fx2 to fx2−skHz, and then increases tofx2+2 kHz. This series of changing the frequency is repeatedsequentially. Directly before terminating the lighting operation of thelighting apparatus, the control circuit 10 stores the above frequencyfx2, in the non-volatile memory, and the control circuit 10 sets thelighting frequency to fx2 at starting the next lighting operation andperforms the lighting operation.

As has been discussed, when the lamp voltage of the high pressuredischarge lamp 8 increases, the lighting frequency is changed within thepredetermined frequency range, the lighting frequency of a point whenthe lamp voltage is the lowest is extracted, and the high pressuredischarge lamp 8 is lit at this lighting frequency. Accordingly, even ifthe resonance-free frequency band is moved due to the aging of the highpressure discharge lamp 8, etc., it is possible to constantly light thehigh pressure discharge lamp 8 in a steady state.

In this way, according to the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method of thepresent embodiment, in addition to the features of the high pressuredischarge lamp lighting apparatuses of the first and the secondembodiments, after lighting the high pressure discharge lamp at apredetermined frequency, the control circuit 10 decreases the frequencyof the high frequency power, increases the high frequency power, andmoves the frequency of the high frequency power to the lightingfrequency that is determined based on the above frequencies. The rangeof this series of changing frequencies is limited, which always preventsthe generation of the acoustic resonance phenomena and enables to lightthe high pressure discharge lamp in a steady state.

Embodiment 4.

The high pressure discharge lamp usually has characteristics that afterthe discharge due to the encapsulated argon gas for about 30 secondsfrom the start of lighting, then metal component such as mercury beginsto evaporate, and the lamp voltage suddenly increases.

In this embodiment, a control method will be explained, for a case inwhich the lighting frequency is set at the starting time so that afterthe discharge due to the argon gas continues, the lighting frequencyreaches a region in which acoustic resonance phenomena occurs.

FIG. 9 shows a circuit configuration of the high pressure discharge lamplighting apparatus according to the present embodiment. Different fromthe circuit configuration of the high pressure discharge lamp lightingapparatus shown in FIG. 1, a resonance strength detecting circuit 11 isnewly added to the circuit configuration of FIG. 9.

Further, FIG. 10 concretely shows relationship among the lightingfrequency and the lamp voltage of a metal halide high pressure dischargelamp having a ceramic arc tube of rated dissipation 35 W and theacoustic resonance phenomena cause by this. As shown in the figure, therelationship can be divided to areas of A, B, C, D, E, F, and Gaccording to the occurrence or the strength of the acoustic resonancephenomena.

Here, the region in which the acoustic resonance phenomena occurs andthe region in which the acoustic resonance phenomena does not occur arereferred to as “resonant region” and “resonance-free region,”respectively. The resonant region is divided into three: high,intermediate, and low according to the strength of the resonance.

First, in the “high resonant region,” the discharge arc violently waversand dies out. And in the “intermediate resonant region,” there are fewpossibilities of dying out of the discharge arc, though the dischargearc wavers. It can be presumed the lighting itself cannot occur in thesetwo resonant regions.

Further, in the “low resonant range,” although the acoustic resonancephenomena rarely occur, the discharge arc is not completely stable andit sometimes flickers. Accordingly, there creates no problem in case ofusing the “low resonant region” when luminous flux rises; however, it isinappropriate to use the “low resonant region” as a region for steadystate lighting of the lamp, since it sometimes gives the user a sense ofdiscomfort.

Under this criteria, the region A is an area which is occupied by thedischarge of argon gas having the lamp voltage of 0V throughapproximately 50V and the region A is also “resonance-free range.” Allthe regions B, C, D, E, F, and G are areas in which the lamp voltage isequal to or greater than approximately 50V, and they are alignedsequentially in this order from the range having the lowest lightingfrequency. They correspond to “high resonant region,” “resonance-freeregion,” “low resonant region,” “intermediate resonant region,”“resonance-free region,” “high resonant region,” respectively.

Further, these regions B through G have features that the frequencytends to decrease at a boundary between the adjacent regions accordingto the increase of the lamp voltage.

In case of FIG. 10, the boundaries between the regions B and C, theregions C and D, the regions D and E, the regions E and F, and theregions F and G are approximated by straight lines having a slope of(−0.17 KHz/V) from basic points of (31 KHz, 50V), (32.5 KHz, 50V), (44.5KHz, 50V), (46 KHz, 50V), (49.5 KHz, 50V), respectively.

The above relationship between the voltage and the frequency is notstrictly defined, but the relationship vary more or less based on avariety or secular changes of the lamps.

The following can be considered as for a reason why the frequency at theboundary decreases as the lamp voltage increases can be considered.

Generally, when the frequency, by which the acoustic resonance phenomenaoccurs, is assumed to be fr, it is known that the frequency fr is inproportion with a product of the speed of sound within the arc tube anda formal factor of the arc tube.

On the other hand, when average molecular weight of gas enclosed in thetube and the absolute temperature are assumed M and T, respectively, itis known that the speed of sound is in proportion with (absolutetemperature T)/(average molecular weight M) to the ½^(th) power.

Here, the changing rate of the absolute temperature T at rising time andthe changing rate of the average molecular weight M are compared, theaverage molecular weight M suddenly increases after the discharge due tothe argon gas, since the encapsulated metal component such as mercury,sodium, thallium, scandium, and dysprosium evaporates, and the changingrate of the average molecular weight M much exceeds the absolutetemperature T. This means (absolute temperature T)/(average molecularweight M) decreases after the discharge due to the argon gas, and thefrequency fr also decreases. As a result, the boundary showscharacteristics that the frequency decreases accompanied to the increaseof the lamp voltage as shown in FIG. 10.

Further, the lamp voltage increases from the starting time and continuesto increase if the lamp voltage avoids passing through the intermediateor high resonant region, and reaches the saturation voltage at which thevoltage cannot increase any more. In FIG. 10, Vs represents a voltagerange (75 through 82V) in which the saturation voltages concentrate. Afrequency range (41 through 45 KHz) of a part, from which the region F(resonance-free region) is cut by the voltage range Vs, is representedby fs.

In order to light the high pressure discharge lamp in a steady statewithout flickering, it is important to control to gather the lampvoltage and the lighting frequency within the region surrounded by thevoltage range Vs and the frequency range fs. L1 shows a track of anoperation point given by the lamp voltage and the lighting frequency ofthe high pressure discharge lamp lighting apparatus according to thepresent embodiment.

In the figure, Vs is set to 75 through 82V; however, Vs may varyaccording to a variety or secular change.

Next, the operation will be explained referring to FIGS. 9 and 10.

The lighting frequency f1 at the starting time is set arbitrarily aroundthe frequency range fs. For the explanation in the present embodiment,the frequency is set in case that the lamp voltage moves from the regionA (resonance-free region) to the region E (intermediate resonant region)through the region D (low resonant region).

First, the control circuit 10 controls the operation of each ofswitching elements 2 a and 2 b with the frequency f1 at the startingtime and keeps this frequency f1 until a switching signal is receivedfrom the resonance strength detecting circuit 11.

The lamp voltage detecting circuit 9 detects an actual value or a peakvalue of the lamp voltage by rectifying, and the lamp voltage detectingcircuit 9 inputs the detected value to the resonance strength detectingcircuit 11. When flickering occurs due to the instabilities of thedischarge arc of the high pressure discharge lamp, the rectified lampvoltage vibrates synchronously to this.

In case of the present embodiment, the flickering begins during theperiod (around the boundary between the region D and the region E) whenthe status moves to the region E (intermediate resonant region) from theregion D (low resonant region) as the lamp voltage increases.

On the other hand, the resonance strength detecting circuit 11calculates amplitude of the voltage change of the lamp voltage, thecurrent of which is made to be direct, and when the calculated amplitudebecomes equal to or greater than a predetermined value, it is judged thewaver of the discharge lamp due to the acoustic resonance phenomena hasthe predetermined value. The resonance strength detecting circuit 11 isset so as to output the switching signal and increase the frequency f1output from the control circuit 10 by the predetermined width of δ f1.

Accordingly, the boundary area is detected by this between the region D(low resonant region) and the region E (intermediate resonant region),and the control circuit 10 switches the lighting frequency from thefrequency f1 to a new frequency f2 (=f1+δ f1 ), which is contained inthe region F (resonance-free region) and outputs. Here, thepredetermined width δ f1 is set to be higher than the frequency width ofthe region E (intermediate resonant region) based on the regionseparation obtained experimentally.

The operation point given by the lamp voltage and the lighting frequencymoves as the region A (resonance-free region)→the region D (low resonantregion)→the region F (resonance-free region); that is, the operationpoint can reach the region for steady state lighting, avoiding to passthrough the intermediate or the high resonant region.

Further, around the boundary between the region D (low resonant region)and the region E (intermediate resonant region), the moment when thevibration of the lamp voltage is detected or the moment when theoperation point passes the region E (intermediate resonant region) issufficiently short from both viewpoints of discharge phenomena andvisual observation, so that the flickering does not become a problem.Although there are various methods to control to gather the lightingfrequencies within the resonance-free region after switching thelighting frequency from f1 to f2, the explanation will be omitted, sincethe methods do not relate to the main theme of the present invention.

As discussed above, the lighting frequency is changed according to thechange of the discharging status at the starting time of the luminousflux to avoid the acoustic resonance phenomena, so that the occurrenceof flickering before reaching the point for steady state lighting can beavoided.

When the boundary area between the region D (low resonant region) andthe region E (intermediate resonant region) is not detected by theresonance strength detecting circuit 11 even if the predetermined timehas passed from the starting time of the lighting operation, the controlcircuit 10 can forcibly switch the lighting frequency from f1 to f2.

In this way, the lighting frequency f1 can be set low at the startingtime. And therefore, in the region D (low resonant region) in which theacoustic resonance phenomena is hard to occur, the control can be surelymoved to the control in the resonance-free region for steady statelighting even if the instabilities of the discharge arc is too small tobe detected, so that the steady state of the lighting can be secured.

Further, in the present embodiment, a case has been discussed, in whichthe lamp voltage has reached the voltage range Vs when the lamp voltagereaches the boundary area between the region D (low resonant region) andthe region E (intermediate resonant region) and the control can besimply switching the lighting frequency from f1 to f2. In the upcomingembodiment, another case will be explained, in which when the lampvoltage reaches the boundary area between the region D and the region E,the control has not reached the voltage range Vs.

As has been discussed, the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method includethe resonance strength detecting means for detecting the rate of theinstabilities of the discharge arc due to the acoustic resonancephenomena based on the change of the lamp voltage by the lamp voltagedetecting means. After starting the operation under the condition thatthe lighting frequency is set by the first frequency which is lower thanthe maximum frequency of a certain frequency range for steady statelighting the high pressure discharge lamp within the resonance-freeregion, when the instabilities of the discharge arc, which exceeds apredetermined extent, is detected by the resonance strength detectingmeans, the control circuit increases the lighting frequency from thefirst frequency by a certain amount and switches to the secondfrequency, which belongs to the resonance-free region. Accordingly, itbecomes possible to surely avoid the flickering due to the acousticresonance phenomena.

When the resonance strength detecting means does not detect theinstabilities of the discharge arc that exceeds the predetermined rateeven if the predetermined time has passed since the lighting operationstarted, the control circuit switches the lighting frequency from thefirst frequency to the second frequency forcibly. Accordingly, it ispossible to avoid misdetection due to a transitional change of the lampvoltage that occurs directly after the lighting operation starts, whichenables to certainly avoid the acoustic resonance phenomena. Further,even if no acoustic resonance phenomena occurs at rising time of theluminous flux, it is possible to move to the control for steady statelighting, which enables to secure the steadiness of the lighting.

Further, after the lighting operation starts under the condition ofsetting the first lighting frequency, which is lower than the maximumfrequency within a particular frequency range, as the lightingfrequency, either when the lamp voltage exceeds the predetermined valueor when the predetermined time has passed since the lighting operationstarts, the control circuit increases the lighting frequency from thefirst frequency by the predetermined amount and switch the lightingfrequency to the second frequency, which belongs to the resonance-freeregion. Accordingly, it is possible to avoid misdetection due to atransitional change of the lamp voltage that occurs directly after thelighting operation starts, which enables to certainly avoid the acousticresonance phenomena and to move to the control for steady statelighting.

Embodiment 5.

In the fourth embodiment, the control method has been explained, inwhich the frequency, which moves from the region A (resonance-freeregion) to the region D (low resonant region) accompanied to theincrease of the lamp voltage, is selected at the starting time. In thepresent embodiment, another case will be explained, in which anotherfrequency that moves from the region A (resonance-free region) to theregion G (high resonant region) through the region F (resonance-freeregion) is selected.

The circuit configuration is the same as one shown in the fourthembodiment and explanation will be omitted here.

In FIG. 11, a locus L2 is added to the segmented regions A through Gshown in FIG. 10, which traces the movement of the operation point basedon the lamp voltage and the lighting frequency of the high pressuredischarge lamp lighting apparatus.

Next, an operation will be explained referring to FIGS. 9 and 11.

That the control circuit 10 controls the operation of each switchingelement at the frequency f1 at the starting time and maintains thisfrequency until the control circuit 10 receives the switching signaloutput from the resonance strength detecting circuit 11, that the lampvoltage rectified by the lamp voltage detecting circuit 9 vibratessynchronously to the instabilities of the arc of the high pressuredischarge lamp, and that the rectified lamp voltage is input to theresonance strength detecting circuit 11 are the same as the fourthembodiment.

As described above, the lighting frequency f1 is set to the frequencythat moves from the region A (resonance-free region) to the region G(high resonant region) through the region F (resonance-free region)according to the rising of the luminous flux (increase of the lampvoltage). The flickering starts from the point when the lamp voltagereaches around the boundary between the region F (resonance-free region)and the region G (high resonant region).

On the other hand, the resonance strength detecting circuit 11calculates amplitude of the voltage variation of the rectified lampvoltage, outputs the switching signal when the amplitude exceeds thepredetermined value, and decreases the frequency f1, which controls theoperation of the switching element, by the predetermined width δ f2.

Consequently, the boundary area between the region F (resonance-freeregion) and the region G (high resonant region) is detected by this, andthe control circuit 10 controls the operation of each switching elementat a new lighting frequency f2 (=f1−δ f2 ), which is included in theregion F (resonance-free region). The control circuit 10 maintains thefrequency f2 until the control circuit 10 receives the switching signalagain. Here, the predetermined width δ f2 is set lower than thefrequency width of the region F (resonance-free region).

In this case, as clearly shown in the figure, since the lamp voltage hasnot reached the voltage range Vs for steady state lighting, the lampvoltage continues to increase, and the boundary area between the regionF (resonance-free region) and the region G (high resonant region) isdetected again. After this detection, when the switching signal isoutput from the resonance strength detecting circuit 11, the controlcircuit 10 decreases the lighting frequency by δ f2 and control theoperation of each switching element with the frequency f3 (=f2−δ f2 )included in the region F (resonance-free region). This operation will berepeated until the lamp voltage reaches the voltage range Vs and getssaturated, and the lighting frequency is switched gradually so as toconstantly stay in the region F (non-resonance region).

In this way, the operation point given by the lamp voltage and thelighting frequency can move as follows: the region A (resonance-freeregion)→the region F (resonance-free region), avoiding to pass throughthe resonant region, and reach the region for steady state lighting.

Although there are various methods of a control for keeping the lightingfrequency within the resonance-free region after reaching the point forsteady state lighting, such a method does not relate to the main purposeof the present invention, and an explanation will be omitted here.However, by performing the above operation repeatedly makes the lightingfrequency stay within the resonance-free region. Accordingly, the aboveoperation can be used for keeping the lighting frequency within theresonance-free region.

As has been discussed, the lighting frequency is made to vary at therising time of luminous flux according to the change of the dischargingstatus to avoid the acoustic resonance phenomena, so that the flickeringduring lighting process of the lamp including status before reaching thepoint for steady state lighting. Further, there is no need to switch thefrequency for passing through the resonant region before reaching thepoint for steady state lighting, and it is possible to reach the pointfor steady state lighting, which enables to rise the luminous flux moresteadily.

In this way, according to the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method, afterthe operation is started with setting the first frequency, which ishigher than the maximum frequency within a particular frequency rangefor steady state lighting the high pressure discharge lamp within theresonance-free region, as the lighting frequency, when the resonancestrength detecting means detects the instabilities of the discharge arcwhich exceeds the predetermined value, the control circuit 10 decreasesthe lighting frequency by the predetermined rate from the firstfrequency and switches to the second frequency which belongs to theresonance-free region. At the same time, within the resonance-freeregion, the control circuit 10 decreases the second frequency graduallyor continuously according to the increase of the lamp voltage.Accordingly, there is no need to dynamically switch the frequency fromstarting the lighting operation up to reaching the steady statelighting, which enables to obtain the rising feature of the luminousflux without visually uncomfortable feeling.

Further, after the operation is started with setting the firstfrequency, which is higher than the maximum frequency within aparticular frequency range for steady state lighting the high pressuredischarge lamp within the resonance-free region, as the lightingfrequency, when the lamp voltage exceeds the predetermined value or thepredetermined time has passed since starting the lighting operation, thecontrol circuit 10 decreases the lighting frequency by the predeterminedamount from the first frequency and switches to the second frequency,which belongs to the resonance-free region. At the same time, within theresonance-free region, the control circuit 10 decreases the secondfrequency gradually or continuously according to the increase of thelamp voltage, so that misdetection due to the initial transitionalchange of the lamp voltage directly after starting the lightingoperation can be prevented. And therefore, the acoustic resonancephenomena can be certainly avoided. Further, there is no need todynamically switch the frequency from starting the lighting operation upto reaching the steady state lighting, which enables to obtain therising feature of the luminous flux without visually uncomfortablefeeling.

Further, the operation of gradually decreasing the second frequency isperformed by the control circuit with repeatedly decreasing the lightingfrequency by the predetermined amount when the resonance strengthdetecting means detects the instabilities of the discharge arc whichexceeds the predetermined rate accompanied to the increase of thelighting frequency, which surely enables to decrease the secondfrequency gradually. Further, there is no need to drastically switch thefrequency from starting the lighting operation up to reaching the steadystate lighting, which enables to obtain the rising feature of theluminous flux without visually uncomfortable feeling.

Embodiment 6.

In the fifth embodiment, the frequency control has been explained whenthe frequency is set to move from the region A (resonance-free region)to the region G (high resonant region) through the region F(resonance-free region) accompanied to the increase of the lamp voltage.In the present embodiment, another control method will be explained, inwhich the operation point given by the lamp voltage and the lightingfrequency follows another locus in the same case with the fifthembodiment.

The circuit configuration is the same as one shown in the fourthembodiment and explanation will be omitted here.

In FIG. 12, a locus L3 is added to the segmented regions A through Gshown in FIG. 10, which traces the movement of the operation point basedon the lamp voltage and the lighting frequency of the high pressuredischarge lamp lighting apparatus.

Next, the operation will be described referring to FIGS. 9 and 12.

That the control circuit 10 controls the operation of each switchingelement at the frequency f1 at the starting time and maintains thisfrequency until the control circuit 10 receives the switching signaloutput from the resonance strength detecting circuit 11, that the lampvoltage rectified by the lamp voltage detecting circuit 9 vibratessynchronously to the instabilities of the arc of the high pressuredischarge lamp, and that the rectified lamp voltage is input to theresonance strength detecting circuit 11 are the same as the fourthembodiment.

On the other hand, the resonance strength detecting circuit 11calculates an amplitude width of the voltage change of the rectifiedlamp voltage, and outputs the switching signal when the amplitudeexceeds the predetermined value, and the control circuit 10 graduallydiminishes the frequency f1 for controlling the operation of eachswitching element. As the control circuit 10 gradually diminishes thefrequency, the flickering occurs around the boundary area between theregion F (resonance-free region) and the region E (intermediate resonantregion) again before long.

Due to this occurrence of the flickering, the boundary area between theregion F (resonance-free region) and the region E (intermediate resonantregion) is detected, and the control circuit 10 controls the operationof each switching element with a new lighting frequency f2 (=f1−fh+δ f3) contained in the region F (resonance-free region). Here, fh means afrequency width of the region F (resonance-free region), and δ f3 meansa frequency increment, which is set lower than the frequency width fh.Both are set based on region segmentation obtained experimentally.

In this case, the lamp voltage also continues to increase as clearlyshown in the figure, since the lamp voltage has not reached the voltagerange Vs for steady state lighting.

Here, the lighting frequency f2 is kept for a predetermined period, andduring which the lamp voltage increases. After keeping for thepredetermined period, using the switching signal output from theresonance strength detecting circuit 11 as a trigger, the frequency isstarted gradually diminishing again. As the frequency is beingdiminished, the frequency of the boundary area between the region F(resonance-free region) and the region E (intermediate resonance region)can be obtained again. The control circuit 10 increases the obtainedfrequency by δ f3 and controls the operation of each switching elementwith the lighting frequency f3 included in the region F (non-resonanceregion).

This operation is repeated until the lamp voltage reaches the voltagerange Vs and gets saturated, and the lighting frequency is switchedgradually so that the lighting frequency fn always stay in the region F(non-resonance region).

By this operation, the operation point, which is given by the lampvoltage and the lighting frequency, can moves to reach the range for thesteady state lighting as follows: the region A (resonance-freeregion)→the region F (resonance-free region), without passing throughthe resonant region.

Although there are various methods of a control for keeping the lightingfrequency within the resonance-free region after reaching the point forsteady state lighting, such a method does not relate to the main purposeof the present invention, and an explanation will be omitted here.However, by performing the above operation repeatedly makes the lightingfrequency stay within the resonance-free region. Accordingly, the aboveoperation can be used for keeping the lighting frequency within theresonance-free region.

As has been discussed, the lighting frequency is made to vary at thestarting time of luminous flux accompanied to the change of thedischarging status to avoid the acoustic resonance phenomena, so thatthe flickering during lighting process of the lamp including a periodbefore reaching the point for steady state lighting. Further, there isno need to switch the frequency for passing through the resonant regionand it is possible to reach the point for steady state lighting, whichenables starting the luminous flux in a steadier state. Further, it ispossible to perform a similar control by extending an interval of theoperation after reaching the point for steady state lighting, whichmakes the lighting frequency constantly stay in the region F(resonance-free region).

According to the present embodiment, the boundary area is detectedbetween the region E (intermediate resonant region) and the region F(resonance-free region) by decreasing the lighting frequency fordeciding the lighting frequency fn (n>2); however, the same effect canbe obtained by detecting the boundary area between the region F(resonance-free region) and the region G (high resonant region) byincreasing the lighting frequency on the contrary and setting thelighting frequency as one that is lower than the boundary by δ f4.

As discussed, according to the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method, theoperation of gradually decreasing the second frequency is performed bythe control circuit with repeatedly decreasing the lighting frequency bythe predetermined amount when the resonance strength detecting meansdetects the instabilities of the discharge arc which exceeds thepredetermined rate accompanied to the increase of the lightingfrequency, which surely enables to decrease the second frequencygradually. Further, there is no need to drastically switch the frequencyfrom starting the lighting operation up to reaching the steady statelighting, which enables to obtain the rising feature of the luminousflux without visually uncomfortable feeling.

Embodiment 7.

In the fifth or the sixth embodiment, the control method has beenexplained, in which the boundary area between the region F(resonance-free region) and the region E (intermediate resonant region)or the region G (high resonant region) is detected, the frequencycorresponding to the boundary area is displaced a little, and thelighting frequency is made to constantly stay within the region F(resonance-free region). In the present embodiment, another controlmethod will be explained, in which the lighting frequency can beconstantly stay within the region F (resonance-free region) withoutdetecting the boundary area.

The circuit configuration is the same as one shown in the fourthembodiment, and an explanation will be omitted here.

In FIG. 13, a locus L4 is added to the segmented regions A through Gshown in FIG. 10, which traces the movement of the operation point basedon the lamp voltage and the lighting frequency of the high pressuredischarge lamp lighting apparatus.

Next, the operation will be described referring to FIGS. 9 and 13.

In the control circuit 10, a conversion equation is previously obtainedfor a locus which follows the operation point given by the lamp voltageand the lighting frequency within the region F (resonance-free region)so that the lighting frequency decreases by an approximately fixedchanging rate in respect of the increase of the lamp voltage, and theconversion equation is stored in a memory in the control circuit 10(which is not shown in the figure).

Then, the lamp voltage detecting circuit 9 confirms that the lampvoltage stays within the region F (resonance-free region), the frequencyis calculated by the conversion equation stored in the memory based onthe lamp voltage, and the lighting frequency is controlled to become thecalculated frequency.

By the above operation, the operation point given by the lamp voltageand the lighting frequency reaches the control F (resonance-freeregion), and then the operation point gradually diminishes accompaniedto the increase of the lamp voltage, while constantly staying in theregion F (resonance-free region).

Namely, the operation point moves as follows: the region A(resonance-free region)→the region F (resonance-free region), and canmove to the steady state lighting, avoiding to pass through the resonantregion.

In the above, a case employing the conversion equation has beenexplained; in another way, a conversion table is previously created andcan be stored in the memory. Although there are various methods of acontrol for keeping the lighting frequency within the resonance-freeregion after reaching the point for steady state lighting, such a methoddoes not relate to the main purpose of the present invention, and anexplanation will be omitted here. However, by performing the aboveoperation repeatedly makes the lighting frequency stay within theresonance-free region. Accordingly, the above operation can be used forkeeping the lighting frequency within the resonance-free region.

As has been discussed, since the lighting frequency is decreasedaccording to the lamp voltage and the acoustic resonance phenomena canbe avoided, which enables to avoid the flickering, including a periodbefore the steady state lighting.

In this way, according to the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method, theoperation of gradually decreasing the second frequency is performed bythe control circuit with repeatedly decreasing the lighting frequency bythe predetermined amount when the resonance strength detecting meansdetects the instabilities of the discharge arc which exceeds thepredetermined rate accompanied to the increase of the lightingfrequency, which surely enables to decrease the second frequencygradually. Further, there is no need to drastically switch the frequencyfrom starting the lighting operation up to reaching the steady statelighting, which enables to obtain the rising feature of the luminousflux without visually uncomfortable feeling.

Further, after the operation starts with setting the first frequency,which is higher than the maximum frequency of a particular frequencyrange for steady state lighting the high pressure discharge lamp withinthe resonance-free region, as the lighting frequency, the lightingfrequency is then decreased at an approximately fixed rate so as to makethe lighting frequency stay within the resonance-free region accompaniedto the increase of the lamp voltage, which enables to certainly avoidthe acoustic resonance phenomena. Further, there is no need todynamically switch the frequency from starting the lighting operation upto reaching the steady state lighting, which enables to obtain therising feature of the luminous flux without visually uncomfortablefeeling.

Embodiment 8.

In the fourth through seventh embodiments, a single algorithm isemployed to avoid the flickering before the steady state lighting. Inthe present embodiment, another frequency control will be explained, inwhich the above operations are combined.

The circuit configuration is the same as shown in the fourth embodiment,and an explanation will be omitted here.

In FIGS. 14 through 16, loci L5 through L7 are added to the segmentedregions A through G shown in FIG. 10, which traces the movement of theoperation point based on the lamp voltage and the lighting frequency ofthe high pressure discharge lamp lighting apparatus.

When the operation point is included in the region A (resonance-freeregion) and the region D (low resonant region), the loci L5, L6, and L7are controlled in the same way explained in the fourth embodiment.

When the operation point moves from the region D (low resonant region)to the region F (resonance-free region), the locus L5 is controlled inthe same way explained in the fifth embodiment; the locus L6 the sixembodiment; and the locus L7 the seventh embodiment.

The operation point given by this with the lamp voltage and the lightingfrequency moves as follows: the region A (resonance-free region)→theregion D (low resonant region)→the region F (resonance-free region), sothat the operation point can move to the steady state lighting withavoiding passing through the intermediate or high resonant region.

A moment when the vibration of the lamp voltage is detected around theboundary area between the region D (low resonant region) and the regionE (intermediate resonant region) or a moment when the operation pointpasses through the region E (intermediate resonant region) is shortenough from a viewpoint of discharge phenomena and visual viewpoint, sothat the flickering never becomes a problem.

As explained above, the lighting frequency is changed according to thechange of the discharge status at rising time of the luminous flux toavoid the acoustic resonance phenomena, which enables to avoid theflickering which may occur before reaching the point for steady statelighting.

Further, by combining plural control algorithms, it is possible tocertainly avoid the flickering before reaching the point for steadystate lighting regardless of the width of the resonant region E(intermediate resonant region) or the region F (resonance-free region).

In the fourth through eighth embodiments, the metal halide high pressuredischarge lamp having the ceramic arc tube of rated dissipation 35W hasbeen explained as an example; however, another high pressure dischargelamp can avoid the flickering before the steady state lighting by thesame control as long as its relationship among the frequency, the lampvoltage, and the acoustic resonance phenomena is similar to the abovemetal halide high pressure discharge lamp.

In the fourth through eighth embodiments, to avoid misdetection, it ispossible to ignore the initial transitional status (e.g., the dischargedue to argon gas) of the starting time. In such a case, it isappropriate to choose an algorithm to control the operation based on theresult detected by the resonance strength detecting circuit 11 withdefining a time when the lamp voltage becomes equal to or greater thanthe predetermined value or a time when a predetermined period has passedfrom starting the lighting operation as the basic point.

In this way, according to the high pressure discharge lamp lightingapparatus and the high pressure discharge lamp lighting method, afterthe control circuit switches the lighting frequency from the firstfrequency to the second frequency, the second frequency is decreasedgradually or continuously according to the increase of the lamp voltage.Accordingly, there is no need to dynamically switch the frequency fromstarting the lighting up to reaching the steady state lighting, whichenables to obtain the rising feature of the luminous flux withoutvisually uncomfortable feeling.

In the foregoing first through eighth embodiments, a half bridge circuitis employed for a high frequency power supplying means; however, acircuit other than the half bridge circuit can be used as long as itsupplies the high frequency power such as a push-pull circuit, asingle-ended voltage resonance circuit, a full-bridge circuit, etc.

INDUSTRIAL APPLICABILITY

According to the present invention, the high pressure discharge lamplighting apparatus, even if the resonance-free frequency band is movedby aging of the high pressure discharge lamp, etc., can supply the highfrequency power having the intermediate frequency of the range to thehigh pressure discharge lamp, which prevents generation of “dying out”or “instabilities” of the discharge arc inside the arc tube and enablesto light the high pressure discharge lamp in a steady state.

1. A high pressure discharge lamp lighting apparatus comprising: a highpressure discharge lamp; a lamp voltage detecting means for detecting alamp voltage of the high pressure discharge lamp; a high frequency powersupplying means for supplying high frequency power to the high pressuredischarge lamp; a control circuit for controlling a frequency of thehigh frequency power supplied by the high frequency power supplyingmeans, wherein the control circuit includes an extracting means forextracting an upper limit frequency and a lower limit frequency ofresonance-free frequency band, and a frequency moving means for changingthe frequency of the high frequency power in a range defined by theupper limit frequency and the lower limit frequency, and for moving thefrequency to a frequency determined based on the upper limit frequencyand the lower limit frequency.
 2. A high pressure discharge lamplighting apparatus comprising: a high pressure discharge lamp; a highfrequency power supplying means for supplying high frequency power tothe high pressure discharge lamp; a control circuit for controlling afrequency of the high frequency power supplied by the high frequencypower supplying means, wherein the control circuit includes: a frequencystoring means for storing a first frequency of a point when a lampvoltage of the high pressure discharge lamp begins increasing when thefrequency of the high frequency power is made to decrease after the highpressure discharge lamp is lit at a predetermined frequency and a secondfrequency of a point when the lamp voltage of the high pressuredischarge lamp begins increasing when the frequency of the highfrequency power is made to increase; and a frequency moving means formoving the frequency of the high frequency power to a third frequencywhich is determined based on the first frequency and the secondfrequency stored in the frequency storing means.
 3. The high pressuredischarge lamp of claim 2, wherein the control circuit limits a movingrange of a series of decreasing the frequency of the high frequencypower after the high pressure discharge lamp is lit at a predeterminedfrequency, increasing the frequency of the high frequency power, andmoving the frequency of the high frequency power to a lighting frequencywhich is determined based on the frequencies.
 4. The high pressuredischarge lamp of claim 2, wherein the frequency moving means repeatedlyperforms a series of operation of moving the frequency of the highfrequency power at a predetermined interval.
 5. The high pressuredischarge lamp of claim 2, wherein the control circuit sets thepredetermined frequency of the point when the high pressure dischargelamp is lit so as to match a lighting frequency of a previous lightingbefore turning-off.
 6. A high pressure discharge lamp lighting apparatushaving: a high pressure discharge lamp; a high frequency power supplyingmeans for supplying high frequency power to the high pressure dischargelamp; a control circuit for controlling a frequency of the highfrequency power supplied by the high frequency power supplying means,wherein the control circuit includes: a lamp voltage storing means forstoring a lamp voltage of a point when the high pressure discharge lampis lit at a predetermined frequency; a frequency storing means forstoring a first frequency of a point when the lamp voltage of the highpressure discharge lamp exceeds the lamp voltage stored in the lampvoltage storing means in case that the frequency of the high frequencypower is made decrease and a second frequency of a point when the lampvoltage of the high pressure discharge lamp exceeds the lamp voltagestored in the lamp voltage storing means in case that the frequency ofthe high frequency power is made increase; and a frequency moving meansfor moving the frequency of the high frequency power to a thirdfrequency which is determined based on the first frequency and thesecond frequency stored in the frequency storing means.
 7. A highpressure discharge lamp lighting apparatus comprising: a high pressuredischarge lamp; a lamp voltage detecting means for detecting a lampvoltage of the high pressure discharge lamp; a high frequency powersupplying means for supplying high frequency power to the high pressuredischarge lamp; a control circuit for controlling a frequency of thehigh frequency power supplied by the high frequency power supplyingmeans, and wherein the high pressure discharge lamp lighting apparatuslights the high pressure discharge lamp in a steady state within aparticular frequency range and a particular voltage range of aresonance-free region which is determined by the lamp voltage and aresonance-free frequency band corresponding the lamp voltage, aresonance strength detecting means for detecting rate of a instabilitiesof discharge arc due to acoustic resonance phenomena based on a changeof the lamp voltage detected by the lamp voltage detecting means, andwherein the high pressure discharge lamp applies a first frequency whichis lower than a maximum frequency of the particular frequency range as alighting frequency at lighting time, and wherein when the resonancestrength detecting means detects the instabilities of the discharge arcwhich exceeds a predetermined rate accompanied to increase of the lampvoltage after lighting, the control circuit increases the lightingfrequency by a predetermined amount from the first frequency andswitches the lighting frequency to a second frequency which belongs tothe resonance-free region.
 8. The high pressure discharge lamp lightingapparatus of claim 7, wherein when the resonance strength detectingmeans does not detect the instabilities of the discharge arc whichexceeds the predetermined rate even if a predetermined time has passedsince starting lighting operation, the control circuit forcibly switchesthe lighting frequency from the first frequency to the second frequency.9. The high pressure discharge lamp lighting apparatus of claim 7,wherein after switching the lighting frequency from the first frequencyto the second frequency, the control circuit gradually or continuouslydecreases the second frequency in respect of an increase of the lampvoltage.
 10. The high pressure discharge lamp of claim 9, wherein thecontrol circuit performs an operation of gradually decreasing the secondfrequency by repeatedly decreasing the lighting frequency by apredetermined amount when the resonance strength detecting means detectsthe instabilities of the discharge arc which exceeds the predeterminedrate accompanied to an increase of the lamp voltage.
 11. The highpressure discharge lamp of claim 9, wherein the control circuit performsan operation of gradually decreasing the second frequency by decreasingthe lighting frequency and then repeatedly increasing the lightingfrequency by the predetermined amount with a predetermined interval whenthe resonance strength detecting means detects the instabilities of thedischarge arc which exceeds the predetermined rate accompanied to adecrease of the tube lighting frequency.
 12. The high pressure dischargelamp of claim 9, wherein the control circuit performs an operation ofcontinuously decreasing the second frequency by controlling to decreasethe lighting frequency with approximately fixed changing rate in respectof an increase of the lamp voltage.
 13. A high pressure discharge lamplighting apparatus comprising: a high pressure discharge lamp; a lampvoltage detecting means for detecting a lamp voltage of the highpressure discharge lamp; a high frequency power supplying means forsupplying high frequency power to the high pressure discharge lamp; acontrol circuit for controlling a frequency of the high frequency powersupplied by the high frequency power supplying means, and wherein thehigh pressure discharge lamp lighting apparatus lights the high pressuredischarge lamp in a steady state within a particular frequency range anda particular voltage range of a resonance-free region which isdetermined by the lamp voltage and a resonance-free frequency bandcorresponding to the lamp voltage, a resonance strength detecting meansfor detecting rate of instabilities of a discharge arc due to acousticresonance phenomena based on a change of the lamp voltage detected bythe lamp voltage detecting means, and wherein the high pressuredischarge lamp applies a first frequency which is lower than a maximumfrequency of the particular frequency range as a lighting frequency atlighting time, and wherein when the lamp voltage detecting means detectsone of that the lamp voltage exceeds a predetermined value afterlighting and that a predetermined time has passed since a lightingoperation has started, the control circuit increases the lightingfrequency by a predetermined amount from the first frequency andswitches the lighting frequency to a second frequency which belongs tothe resonance-free region.
 14. A high pressure discharge lamp lightingapparatus comprising: a high pressure discharge lamp; a lamp voltagedetecting means for detecting a lamp voltage of the high pressuredischarge lamp; a high frequency power supplying means for supplyinghigh frequency power to the high pressure discharge lamp; a controlcircuit for controlling a frequency of the high frequency power suppliedby the high frequency power supplying means, and wherein the highpressure discharge lamp lighting apparatus lights the high pressuredischarge lamp in a steady state within a particular frequency range anda particular voltage range of a resonance-free region which isdetermined by the lamp voltage and a resonance-free frequency bandcorresponding to the lamp voltage, a resonance strength detecting meansfor detecting rate of instabilities of a discharge arc due to acousticresonance phenomena based on a change of the lamp voltage detected bythe lamp voltage detecting means, and wherein the high pressuredischarge lamp applies a first frequency which is lower than a maximumfrequency of the particular frequency range as a lighting frequency atlighting time, wherein when the resonance strength detecting meansdetects the instabilities of the discharge arc which exceeds apredetermined rate according to increase of the lamp voltage afterlighting, the control circuit decreases the lighting frequency by apredetermined amount from the first frequency and switches the lightingfrequency to a second frequency which belongs to the resonance-freeregion and makes the second frequency gradually or continuously decreasein respect of the increase of the lamp voltage within the resonance-freeregion.
 15. A high pressure discharge lamp lighting apparatuscomprising: a high pressure discharge lamp; a lamp voltage detectingmeans for detecting a lamp voltage of the high pressure discharge lamp;a high frequency power supplying means for supplying high frequencypower to the high pressure discharge lamp; a control circuit forcontrolling a frequency of the high frequency power supplied by the highfrequency power supplying means, and wherein the high pressure dischargelamp lighting apparatus lights the high pressure discharge lamp in asteady state within a particular frequency range and a particularvoltage range of a resonance-free region which is determined by the lampvoltage and a resonance-free frequency band corresponding to the lampvoltage, a resonance strength detecting means for detecting rate ofinstabilities of a discharge arc due to acoustic resonance phenomenabased on a change of the lamp voltage detected by the lamp voltagedetecting means, and wherein the high pressure discharge lamp applies afirst frequency which is lower than a maximum frequency of theparticular frequency range as a lighting frequency at lighting time, andwherein when the lamp voltage detecting means detects one of that thelamp voltage exceeds a predetermined value after lighting and that apredetermined time has passed since a lighting operation has started,wherein when the resonance strength detecting means detects theinstabilities of the discharge arc which exceeds a predetermined rateaccording to an increase of the lamp voltage after lighting, the controlcircuit decreases the lighting frequency by a predetermined amount fromthe first frequency and switches the lighting frequency to a secondfrequency which belongs to the resonance-free region and makes thesecond frequency gradually or continuously decrease in respect of theincrease of the lamp voltage within the resonance-free region.
 16. Ahigh pressure discharge lamp lighting apparatus having: a high pressuredischarge lamp; a lamp voltage detecting means for detecting a lampvoltage of the high pressure discharge lamp; a high frequency powersupplying means for supplying high frequency power to the high pressuredischarge lamp; a control circuit for controlling a frequency of thehigh frequency power supplied by the high frequency power supplyingmeans, and wherein the high pressure discharge lamp lighting apparatuslights the high pressure discharge lamp in a steady state within aparticular frequency range and a particular voltage range of aresonance-free region which is determined by the lamp voltage and aresonance-free frequency band corresponding to the lamp voltage, whereinthe high pressure discharge lamp applies a first frequency which ishigher than a maximum frequency of the particular frequency range as alighting frequency and decreases the lighting frequency at approximatelyfixed rate so as to stay within the resonance-free region in respect ofan increase of the lamp voltage.
 17. A method for a high pressuredischarge lamp lighting having: a high pressure discharge lamp; a lampvoltage detecting step for detecting a lamp voltage of the high pressuredischarge lamp; a high frequency power supplying step for supplying highfrequency power to the high pressure discharge lamp; a control step forcontrolling a frequency of the high frequency power supplied by the highfrequency power supplying means, the method further comprising: anextracting step for extracting an upper limit frequency and a lowerlimit frequency from a resonance-free frequency band, wherein thecontrol step changes a frequency of the high frequency power within arange defined by the upper limit frequency and the lower limit frequencyof the resonance-free frequency band extracted by the extracting means,and then moves to a predetermined frequency which is determined based onthe upper limit frequency and the lower limit frequency.